Zeolites are crystalline aluminosilicate molecular sieves which have a microporous three-dimensional framework structure. In general, the crystalline zeolites are formed from corner-sharing AlO.sub.2 and SiO.sub.2 tetrahedra and are characterized by having pore openings of uniform dimensions, having a significant, ion-exchange capacity and being capable of reversibly desorbing an adsorbed phase which is dispersed throughout the internal voids of the crystal without significantly displacing any atoms which make up the permanent crystal structure.
Other crystalline microporous compositions are known which are not zeolitic, i.e., do not contain AlO.sub.2 tetraheda as essential framework constituents, but which exhibit the ion-exchange and/or adsorption characteristics of the zeolites. These include: 1) crystalline aluminophosphate compositions disclosed in U.S. Pat. No. 4,310,440; 2) silicon substituted aluminophosphates as disclosed in U.S. Pat. No. 4,440,871; 3) metal substituted aluminophosphates as disclosed in U.S. Pat. No. 4,853,197; 4) metal sulfide molecular sieves disclosed in U.S. Pat. No. 4,880,761 and 5) metallo zinc-phosphate compositions disclosed in U.S. Pat. No. 5,302,362. There are also various reports of zirconium silicate molecular sieves. U.S. Pat. No. 5,015,453 discloses zirconium, hafnium or titanium silicates containing both octahedral and tetrahedral framework units. In U.S. Pat. No. 4,705,675 it is disclosed that metals such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Zr or Y can be inserted into the crystal structure of a zeolite. It is also stated that these metals are introduced as tetrahedral units. Zirconium silicates having the MFI and MEL structures have also been reported in Stud. Surf. Sci. Catal, 83 (Zeolites And Microporous Crystals), 57-66 (1994) and J. of Catalvsis, 163, 501-505 (1996). It is stated in these publications that zirconium is tetrahedral. A zirconium silicate identified as ZRSI-1 is disclosed in U.S. Pat. No. 5,338,527.
There are also numerous other reports of zirconium silicates including minerals and synthesized compositions. These include: 1) Na.sub.2 ZrSi.sub.3 O.sub.9.2H.sub.2 O (catapleiite), Na.sub.2 ZrSi.sub.6 O.sub.15.3H.sub.2 O (elpidite), Na.sub.3 ZrSiO.sub.6 (O/OH).sub.18 (lovozerite), Na.sub.2 ZrSi.sub.2 O.sub.7 (parakeldyshite), Na.sub.2 ZrSi.sub.4 O.sub.11 (vlasovite), Na.sub.2 ZrSiO.sub.5, Na.sub.6 Zr.sub.2 Si.sub.4 O.sub.15, Na.sub.4 ZrSi.sub.5 O.sub.16, Na.sub.14 Zr.sub.2 Si.sub.10 O.sub.31, disclosed in C.R. Acad. Sc. Paris, 278, 689 (1974); 2) K.sub.2 ZrSi.sub.3 O.sub.9 (wadeite) disclosed in Contrib. Mineral. Petrol, 72, 191 (1980); 3) K.sub.2 ZrSi.sub.6 O.sub.15 (dalyite) in C.R. Acad. Sc. Paris, 270, 2741 (1970); 4) Na.sub.2 ZrSi.sub.3 O.sub.9.2H.sub.2 O (gaidonnayite) in Can. Mineral, 12, 143-144 (1973); 5) Na.sub.2 ZrSi.sub.3 O.sub.9.3H.sub.2 O (hilairite) in Can. Mineral., 12, 237 (1974); 6) (Na/H).sub.2 ZrSi.sub.2 O.sub.7 (keldyshite) Na.sub.4 Zr.sub.2 Si.sub.5 O.sub.16, lzvestiva Akademii Nauk SSSR, Neorganicheskie Materialy, 6, (11), 2081-2083 (1970); 7) K.sub.2 ZrSi.sub.2 O.sub.7 (khibinskite), Sov. Phys. Dopl., 15, 711 (1971); 8) K.sub.4 Zr.sub.2 Si.sub.6 O.sub.8.2H.sub.2 O (kostylevite), Zup. Vses. Mineral. O-Va., 112, 469 (1983); 9) K.sub.3 Zr.sub.2 H(Si.sub.3 O.sub.9).sub.2.2H.sub.2 O (paraumbite), K.sub.2 ZrSi.sub.3 O.sub.9.2H.sub.2 O (umbite), Neorganisheskie Materialy, 29 (7), 971 (1993); 10) Na.sub.5 Zr.sub.2 Si.sub.6 O.sub.18 (CI/OH).2H.sub.2 O (petarasite), Can. Mineral., 18, 497 (1980); 11) LiNaZrSi.sub.6 O.sub.15 (zektzerite), Powder Diffraction, 2 (3), 176 (1987); 12) Na.sub.4 Zr.sub.2 Si.sub.3 O.sub.12 in J. Solid State Chem., 39, 219-229 (1981); 13) Na.sub.4 ZrSi.sub.3 O.sub.10 in Solid State Ionics, 7, 345 (1972); and 14) K.sub.2 ZrSiO.sub.5 in Inorg. Mater. (Engl. Transl.) 9 (1), 117 (1964).
Finally, zirconium silicates are disclosed in PNNL-11451 report entitled, "Efficient Separations and Processing. Crosscutting Program: Develop and Test Sorbents", G. N. Brown, Principal Investigator, Pacific Northwest Laboratory, 1996 Annual Progress Report.
In contrast to this art, applicants have developed a family of molecular sieves which have octahedral ZrO.sub.3 units and tetrahedral SiO.sub.2 units and an empirical formula on an anhydrous and as synthesized basis of : EQU A.sub.p M.sub.x Zr.sub.1-x Si.sub.n O.sub.m
where A is an exchangeable cation such as sodium or potassium ion, M is a framework metal such as tin or titanium, "p" has a value from about 1 to about 6, "x" has a value from greater than zero to less than 1, "n" has a value from about 2 to about 4, "m" has a value from about 7 to about 12. These compositions have an intracrystalline pore system allowing them to selectively exchange ions. In fact, applicants have determined that this family of molecular sieves can selectively exchange ammonium ions in the presence of calcium ions.